I just bought two 1 ton chain hoists that I would like to mount in the rafters of the shed that is built off the side of my shop. I plan to use them to each lift one end of my Rhodes 18 and other small boats as needed. I have 2 x 10 rafters on a 5/12 pitch with a 12' span. They are hung off the shop with joist hangers and supported by a wall on the other end. There is a 3/4" space above them because of the strapping that runs lengthwise that the metal roof is fastened to.

I'd like to drill a hole near the top of each rafter big enough to slide a 3/4" x 20' black iron pipe into so that I could hang the chain hoists anywhere along the pipe. Do you think that would weaken the rafters too much?

Mrleft8

11-30-2007, 09:13 PM

Yes.
And 3/4" black pipe is kinda skimpy for the load you're talking about...... Unless you plan on ventilating your tin roof as you work....

Ian McColgin

11-30-2007, 09:30 PM

3/4" might be a bit light were you actually lifting a 4000# object. The Rhodes is nowhere near that.

Get a good table book to be sure, but I think this will work.

Ah, screw the tables - real engineers break stuff.

Ian McColgin

11-30-2007, 09:58 PM

I think the rafters are 12' long, not 12' apart.

The Rhodes is barely 800# and as lifted, sans CB and other gear, probalby only 600# - barely 300# per hoist. Hard to have much trouble here.

George Ray

11-30-2007, 10:02 PM

Sister the rafters (assume rafters on 16" or 24" centers) where you drill the hole for the pipe. The pipe size (swag) 1 1/2" schd 80. The sisters will provide the rafters sufficient strength to be rafters again but not necessarily to support the tons of stuff you will hang.
You can make some of the sisters extra long and maybe even double sisters (both sides of rafter) so the effect is something like an 8' long 5 x 10 beam at that particular spot. When you are going to do a heavy lift, hang the chain fall as close as possible to one of the heavy sistered rafters and place a couple of posts ( 2x4 or 4x4) at either end of the sistered span and you can lift to you hearts content.

KMacDonald

11-30-2007, 11:12 PM

It would hardly weaken the joists at all if you drilled the holes in the vertical center on the joists. The top of the joists are in compression and the botom of the joists are in tension when a downward force is applied. The center has no force a all. You would need access to one end to be able to slide the pipe through. Thick walled pipe spanning 16" or 24" would easily support your boat but not 4000lbs.

JMAC

12-01-2007, 12:40 AM

The rafters are 24" on Center and the pipe would go through each of them so that the longest pipe span would be 22 1/2". I'm probably wrong but I thought if you put a hole in a rafter or joist then it only had as much strength as the width from the edge of the hole to the edge of the plank.

I lifted the boat with blocks hung from one rafter on each end a couple of years ago and the building didn't come down, and I think that having the pipe in there will spread the load to put less strain on the individual rafters.

But really, KMacdonald, I should drill through the center? Here's the boat in question... http://farm3.static.flickr.com/2201/2077166752_43557c1106.jpg?v=0

StevenBauer

12-01-2007, 01:29 AM

I agree with K, dril the holes in the center of the joists. All the stresses are in the top and bottom of the stick. Think about trusses or those wood I-beams.

Steven

KMacDonald

12-01-2007, 05:22 AM

Yes, drill in the center. Almost no loss in strength.

KMacDonald

12-01-2007, 05:25 AM

SB is correct. The wood I-beams or "TJI's" have the centers drilled out with 8" or 9" holes for HVAC duct work. This is the same principle with dimensional lumber.

Ian McColgin

12-01-2007, 05:38 AM

For the engineers, isn't there a difference between a hole in an I beam and a force vector located at that hole either normal or nearly normal to the beam.

I for one have seen a rod placed through a rafter from which a tackle was hung simply split and break the lower half of the rafter with a good load. Putting the rod near the top of the rafter solved that.

KMacDonald

12-01-2007, 06:34 AM

With the holes in the middle, the joists would act as if they were half the heigth of the full joist for supporting the hoist (10"-3/4")/2. With the light loads of his boat this is not a concern. As when lifting any heavy load, dont stand directly under it. With the holes in the middle, the original capacity of the joist is not compromised.

PeterSibley

12-01-2007, 06:36 AM

The load would act on the top and bottom of the rafter even if the load is on the top and not causing a potential split has to be an advantage .

George Ray

12-01-2007, 06:38 AM

Short plywood (3/8") sister patches applied both side of rafter at hole site (full 10" rafter width and about 16" long) with yellow glue and small 3d CC box nails will overcome any local defects in the grain of the rafter and allow shifting the hole above or below the center point (neutral axis) with affecting overall beam carrying capacity. Will also avoid the splitting scenario that Ian_C rightfully points out.

Andreas Jordahl Rhude

12-01-2007, 08:52 AM

I'd at least double your rafter. Add another one right beside the existing and support it on each end just like the others. Nail the two together to form a homogenous piece. And drill your hole in the center of the depth. Keep the hole diameter to a minimum, just enough to fit what ever you're putting thru it.

Andreas

RT MAN

12-01-2007, 08:58 AM

Sister the rafters (assume rafters on 16" or 24" centers) where you drill the hole for the pipe. The pipe size (swag) 1 1/2" schd 80. The sisters will provide the rafters sufficient strength to be rafters again but not necessarily to support the tons of stuff you will hang.
You can make some of the sisters extra long and maybe even double sisters (both sides of rafter) so the effect is something like an 8' long 5 x 10 beam at that particular spot. When you are going to do a heavy lift, hang the chain fall as close as possible to one of the heavy sistered rafters and place a couple of posts ( 2x4 or 4x4) at either end of the sistered span and you can lift to you hearts content.

I would just hoop a chain or heavy nylon webbing (sling) around the rafter rather than drill a hole, the whole will creat a weak point right where your putting all the load.

StevenBauer

12-01-2007, 09:25 AM

J, in the new issue of Small Boats Ben Fuller has an article about storing boats. He describes a really cool system: a pipe was installed through a hole in the rafters like you are planning, but instead of using chain hoists there is a big crank on one end and some webbing wrapped around the shaft. Just loop the webbing under the boat and crank away. :) Once it's up there secure with appropriate straps.

Steven

JMAC

12-01-2007, 09:33 AM

I found out this morning that the hook on top of the chain hoist doesn't fit over a 3/4" pipe....almost....but it won't. I plan to make a loop of heavy chain to go around the pipe and hook onto that.

RT Man- I did that originally and it worked, but it didn't seem like the rafter was very happy about it. My hope with the pipe is to get versatility in placing the hoist and to spread the load to more than one rafter.

Steven- how do you like Small Boats? Does it overlap WoodenBoat a lot?

StevenBauer

12-01-2007, 09:48 AM

I like Small Boats. :) This years issue especially. It was great seeing Gavin rowing the boat we built together. I haven't finished reading the whole issue yet.

Steven

ssor

12-01-2007, 09:51 AM

Rafter sizes are figured for about 40 pounds per square foot of roof. They aren't expected to carry a concentrated load. At the very least double them for their entire length. Use a flat plate 1/2 inch thick and 3-4 inches wide laid across the tops with a good stout "D" ring or a webbing sling on the plate. That way you won't have to worry if you need to crawl under the load when there is 3 feet of snow on the roof. Any welding shop can provide you with the steel you need. One ton is a serious load, figure ten men all standing close together on the roof.

George Roberts

12-01-2007, 10:38 AM

I think that hanging a boat from this roof is a poor idea. The roof was not designed for that usage.

Much better to put in a couple new beams supported by posts.

Bill Perkins

12-01-2007, 10:56 AM

Jmac ; for the infrequent occasions when you need to lift , I would make up a couple of 4by4 posts with the correct angled seat cut sawn in to support a doubled rafter (2 in. deep seat , 1 1/2 in. runs up side of rafter , or, one full length 2by4 and 2 supporting jack studs ) . A single 1/2 in. bolt would connect the vertical post to the doubled rafter . A sling placed over the rafter "down hill" from the post would hold the chain hoist for that end of the lift . No significant extra loads would be placed on the rafter's connection to the barn ( a possible weak point ). The post would be placed to shorten the span of the rafter as much as practical , and the sling would be set as close to the post as practical .

You could be no further than about 6 inches from a perfect fore and aft vertical alignment with the hoisted boats's lifting points . I don't think you need the pipe. Choose the supporting rafters so that any slight misalignment draws the supporting rafters toward each other ,adding solid blocking between rafters to pick up that load . I would add solid blocking at the supporting wall as well . For boats of different lengths you would simply shift one of the posts to a different rafter . When not needed for lifting ,both posts would be removed and stored .

The bolt hole would be placed at mid depth on the rafter so its normal function would not be compromised . The sling would be positioned over the boat's centerline of course ; maybe an 8 in. length of all thread bolted through the joist there would be used to prevent the sling from slipping downhill.

Thorne

12-01-2007, 12:03 PM

I've been dealing with a similar issue -- the desire to hoist a lighter boat (350lbs?) up about 3' from lighter (and much older) garage rafters.

First, I've no experience with chain hoists, but can we assume that they lower under weight as well as they lift? I tested lifting with dual comealongs, and even with one set opposite the other, the release/lowering was much too exciting.

Second, won't jmac want to set up a strongback/beam (can't think of the proper name, it is early and the coffee hasn't kicked in yet)? That way the lifting/lowering force would be transferred to blocks on the beam, and the beam then has the two or three support straps that connect directly to the boat.

Third (we are all guessing here without photos), it sure seems that 3' ply sisters glued and screwed to either face of the beams with the holes drilled through all three would provide quite a bit of additional strength across the structure.

The need for additional vertical support to a fully sistered rafter (possibly via the 4x4 posts suggested by Bill) might need to be determined by trial and error, or a visual check of the entire internal structure with a similar weight hoisted and hanging.

These are all great ideas, and I may try 'em in my elderly garage. First I'll need to test some light chain hoists to understand how they control the decent of weight...

David G

12-01-2007, 12:16 PM

Having been a professional woodworker for 30+ years - and self-employed for more than half that time, I've done a bit of rigging and jackleg engineering. It'd be nice to have some fotos of the setup you have. Trying to visualize it, two issues come to mind that haven't been addressed. First is the joist hangers. I'm thinking if you're going to put extraordinary loads on the structure, those joist hangers alone might not be adequate to carry one end of each rafter. Maybe a cleat (2X2 or 2X4) running under the shop end of the joists and attached to the studs in the shop wall? Second is the potential racking forces. Is there any sort of blocking between the rafters to keep them from flopping over? Maybe there should be.

The issue of piercing your rafters I can't answer offhand. All my reference books are down at the shop. I will say two things about it. First, my initial reaction is: I wouldn't be inclined to do it. I don't like putting holes in structural members unless absolutely necessary. Second, I'd be willing to consider it only with clear, authoritative information in hand about how to do so. That doesn't mean: you think it'll probably work; a bunch of us yobs here on the forum think you're probably right; you proceed. It does mean: primary research. Look it up for yourself. Go to the library. BTW, the Navy publishes an interesting book on small construction & rigging which I've found quite handy over the years. Or, search the net for Reliable Information. Remain skeptical - remember, it's you who'll be fixing the roof if you rip it up, or the boat if you drop it. Maybe it's just me, but words are inadequate to describe how much I abhor and detest doing repairs that were avoidable.

<Grouch, grump, grumble>

Hughman

12-01-2007, 12:51 PM

First; You know you will want to hoist more weight than the boat eventually.

Sister the joists, at least the ones on either side of the chain. Back up the hangers, as per David; Add collar ties - the load offers an outward force which must be countered. Finally, add trianglular plywood gussets at the peak, both sides of the rafter. This ties the rafters together - they may be in compression, but when they fail, they will twist past each other, as the walls flatten outward. Additional support posts are belt and suspenders, but they will only help with a single force vector, and get in the way. Better to use an "A" frame, but now you don't have room to move!

It won't be the evenly balanced load that causues failure, but unequal racking force, including shock loads. Also imagine 10" of wet snow on the roof while things are suspended.

David Conard

12-01-2007, 12:58 PM

I second Bill's and David G's suggestion of blocking or bridging between the joists. It is a good way to not only prevent twist in the rafter, but also to spread the load across several rafters. Given the rather modest load you are describing, I would go with a row of bridging along the mid-point of the rafters (near where you will put your chain over a renforced rafter) and a 2 x 4 ledger along the wall under the top ends of the rafters.

Wood has higher strength in compression than tension and wooden beams usually fail on the tension side (bottom in this case)

A rule of thumb is that the strength of a beam increases by the square of its depth. Sistering or doubling will only do that - double the strength. If you can increase the depth your gains can be much greater. A little math goes along way here.

A method to increase the strength of the beam for this application would be to attach a tension member on the lower side of each joist effectively creating an upside down T-shaped beam. Steel strapping might serve here.

I would not hang anything normal (90į) to the neutral axis on a wooden beam.

Pipe makes a good column but an unfortunate beam; it is missing material in exactly the wrong places (tension side and the compression side)

I might consider using a small short piece of modified steel I beam (upper flanges extended to be hanging from the upper edges of any two reinforced joists and a hole for the hook) and live with the limitation of a hook every two feet.

ssor

12-01-2007, 02:15 PM

Before you decide to go ahead with this projact consider this link.
http://www.raisedfloorliving.com/spantables-1.shtml

JMAC

12-01-2007, 02:50 PM

I'm going into town in a while and will try to get a new SD card so that I might get pictures onto the site here.

So you know, I don't anticipate leaving things hanging for long. My plan would be to raise the boat with the hoists and a continuous loop of rope around the hull at either end. Then pull the trailer out, swing the boat upside down, then lower it down onto sawhorses. Don't tell me it won't work, as I've done it using blocks hanging from individual rafters in this same shed. I'm now looking to improve the system and a lot of the above suggestions seem to be good ones.

The Bigfella

12-01-2007, 03:32 PM

I don't anticipate leaving things hanging for long.

Buy two cartons of beer and a couple of pounds of sausages. Round up six or eight guys, lift, drink and eat.

ssor

12-01-2007, 04:12 PM

The one ton hoists kinda threw us off. The weak link in your systen will be your rope most likely. Just don't try to check the capacity of those hoists without doing some serious reinforcements on the roof structure.

Hughman

12-01-2007, 04:50 PM

I bet you knew we'd have you build a whole new workshop out of bridge steel and hardwood timberframe, with concrete walls, laminated buttresses, hydraulic lifts and walk in refrigerator, didn't you?

KMacDonald

12-01-2007, 07:01 PM

Just make it easy. Add a 2 x 8 bridge with joist hangers between two joists. Screw a lag screw hook to the bottom of the bridging and hang the hoist. We are not talking about a lot of weight here. I assume you are not storing the boat from the hoist, just turning it or adjusting trailer bunks etc. I have seen fools lift 1000lb engines from a 2 x 4's laid across 2 x 4 truss cords and they didnt even break.....not recommended.

Peter Malcolm Jardine

12-01-2007, 07:09 PM

The real way to make a travelling hoist is to use a chunk of I Beam running the length of what you choose to move the hoists. It's relatively easy to strengthen the rafter to hold as much weight as you plan to lift, but the key is to get not only versatility, but the ability to move the hoists small distances with great accuracy. Usually a car is mounted on the I beam,and the hoist hangs from the car.That allows the hoist to move even an inch with relative ease.

Ken Hutchins

12-01-2007, 07:13 PM

This going to turn into another Jorgies thread.:D:D Which is one option,:) the other option barn door track and trolleys.:D
Either option is fine if you know what you are doing.